Generally, liquid ejection recording heads (including ink jet recording heads and ink jet heads) employing a liquid ejection recording system (including an ink jet recording system) comprise a plurality of tiny discharge ports, a plurality of flow paths and a plurality of liquid discharge means provided along part of these flow paths. In order to eject ink from the liquid ejection recording head onto recording paper to obtain high quality images, it is preferable that the same volume of ink be discharged at the same discharge speed from the individual discharge ports. Further, the shape of the boundary face between each discharge port and the corresponding communication flow path must not adversely affect the discharge of ink.
As a method for manufacturing an ink jet recording head, a method is described in Japanese Patent Application Laid-Open No. H06-286149, according to which an ink flow path pattern is formed by using a dissolvable resin, and is coated by an epoxy resin, and, thereafter, discharge ports are formed and the dissolvable resin is removed. Further, another method is disclosed in Japanese Patent Laid-Open Application No. 2001-179990, according to which a substance that inhibits photo curing of a discharge port formation material is mixed with a removable resin.
For the discharge of extremely small droplets, a liquid flow resistance at the discharge port of the liquid ejection recording head must be reduced, and the liquid ejection speed must be maintained. In Japanese Patent Laid-Open Application No. 2003-25595, an idea is disclosed according to which two layers of dissolvable resin are formed, and an intermediate portion (an intermediate chamber), narrower than substrate flow paths and wider than distal ends of the discharge ports, is provided between the substrate flow paths and the distal ends of the discharge ports.
Recently, as the image quality of ink jet (IJ) printers has become highly competitive, the size of ink droplets to be discharged has been reduced. And as the size of ink droplets has been reduced, the diameter of the orifice (the diameter of the discharge port, of the IJ head) that discharges ink droplets has also become smaller. However, in the cross section of a conventional IJ head shown in FIG. 13A, when the diameter of a discharge port 909 is reduced without its thickness PH (OP thickness) being changed, the flow resistance of ink at the discharge port 909 is increased in proportion to the square of the diameter of the discharge port 909. As a result, when the discharge of ink is started, following a pause, e.g., after the printer has been halted, the characteristic of the discharge of ink droplets tends to be deteriorated at the first discharge (this phenomenon is called an “incomplete discharge phenomenon”). It should be noted that in FIGS. 13A to 13C the other components are a substrate 901, a heat generating resistor 902 and a flow path formation member 907 and that MH denotes a flow path height.
In order to stably launch small droplets, the present inventors attempted to manufacture a small droplet nozzle wherein, as shown in FIGS. 13B and 13C, the diameter of a discharge port was small and the OP thickness (PH) was reduced (e.g., about PH≦10 μm) When this ink jet recording head was manufactured, however, using the methods described in the above-described patent publications, new technical problems were found.
Specifically, as one phenomenon, a scum occurs at the interface between a removable resin and a discharge port formation material used for forming ink discharge ports, and the direction in which ink droplets are ejected from the discharge port faces is bent, so that a printed image is deteriorated. This phenomenon could not be resolved using the method disclosed in Japanese Patent Laid-Open Application No. 2001-179990.
The present inventors thoroughly studied this phenomenon and arrived at the following conclusion. The discharge port formation material is a negative type resist, and the discharge ports are formed during the photolithography process. That is, since the negative type resist is employed to form a cured layer, including discharge ports, UV light irradiation is performed through a mask (not shown) for an area other than the discharge ports. At this time, the amount of light irradiating a unit area is larger in an area wherein the removable resin is present than in an area wherein the resin is not present. When the diameter of a discharge port is small, during light irradiation, the amount of light (per unit area) that reaches an unexposed portion (a discharge port area) is increased.
As a result, for a shape wherein the flow path height is extended and the PH (OP thickness) is thin, the difference in the amount of irradiated light is increased even more. Through an analysis of the cross-section of the minute discharge port, it was found that the scum can be clearly observed at the interface between the removable resin and the discharge port formation material used for forming ink discharge ports.
Based on the above new view, the present inventors realized that there was a problem with the complete removal of a scum that occurs at the interface between a removable resin and a discharge port formation material, used for forming ink discharge ports having the nozzle shape of an IJ head, as shown in FIGS. 13B and 13C, whereat the difference in the amount of irradiated light is increased.